Circuit breaker with arc-extinguishing means



Nov. 16, 1965 H. D. DORFMAN ETAL 3,218,418

CIRGUITVBREAKER WITH ARC-EXTINGUISHING MEANS NOV- 15, 1965 H. D. DORFMAN ETAL 3,218,418

CIRCUIT BREAKER WITH ARC-EXTINGUISHING MEANS Filed May 19, 1961 4 Sheets-Sheet 2 l NOV- 15, 1965 H. D. DORFMAN ETAL 3,218,418

CIRCUIT BREAKER WITH ARC-EXTINGUISHING MEANS Filed May 19, 1961 4 SheeS-Shee 3 N0V 16, 1955 H. D. DORFMAN ETAL 3,218,418

CIRCUIT BREAKER WITH ARG-EXTINGUISHING MEANS Filed May 19. 1961 4 sheets-sheet 4 Fig. I5 |75 Fig. I8 |75 IGI 6' Fig. I9 Fig. 2O

United States Patent O 3,218,418 CIRCUIT BREAKER WITH ARC-EXTINGUISHING MEANS Hiller D. Dorfman, deceased, late ofBeaver, Pa., by Minnie R. Dorfman, administratrix, Beaver, Pa., and Gerald J. Freese, Beaver, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed May 19, 1961, Ser. No. 112,172 2 Claims. (Cl. 20G-444) This invention relates to circuit breakers and more particularly to circuit breakers of the type comprising contacts separable to establish an arc and an arc-extinguishing unit for extinguishing the arc.

In certain types of circuit breakers, particularly circuit breakers of the molded insulating case type, it is desirable to have a unitary circuit-breaker mechanism that can be assembled, tested and calibrated before it is mounted in the case or housing. A satisfactory separate unitary circuit-breaker mechanism that includes an arc extinguishing unit has not been provided in the prior art.

Accordingly, an object of this invention is to provide an improved circuit breaker that comprises a separate unitary circuit-breaker mechanism that includes an arc extinguishing unit.

Another object of the invention is to provide a circuit breaker comprising an insulating housing and a circuitbreaker mechanism that is supported between two insulating side plates within the housing, which circuit-breaker mechanism includes an arc-extinguishing unit comprising a plurality of arc-extinguishing plates which are so supported between the insulating side plates that the insulating side plates function as side walls of the arc-extinguishing unit.

A more general object of the invention is to provide an improved circuit breaker that is easier to manufacture and assemble.

A further object of the invention is to provide an improved multipole circuit breaker that comprises two or more single pole breakers with improved means for operatively connecting the single pole breakers.

Other objects of the invention will be explained fully hereinafter or will be apparent to those skilled in the art.

According to one embodiment of the invention, there lis provided a circuit breaker comprising an insulating housing and a circuit-breaker mechanism disposed within the housing. The circuit-breaker mechanism is a unitary structure that comprises two insulating side plates having supported therebetween a pair of separable contacts that are manually controlled by means of an operating mechanism, which contacts are automatically opened by operation of a tripping mechanism. The contacts, operating mechanism and tripping mechanism are all supported by the two insulating side plates. The insulating side plates also support a plurality of conducting plates to thereby provide an improved arc-extinguishing structure for extinguishing the arc drawn when the contacts are separated. Thus, the complete circuit-breaker mechanism can be assembled, tested and calibrated as an operating unit before it is mounted in the insulating housing.

In order to connect two or more of the circuit breakers to function as a multipole circuit breaker a knockout is removed from one wall of each of the circuit breakers. The two breakers are placed in a side-by-side abutting relationship and the trip members of the adjacent breakers are connected, to function as a unitary tripping structure, by means of a trip bar connecting member that lits in the openings provided by the removal of the two knockouts. The two breakers are riveted together and one or more handle ties are provided so that all the handles will be 3,218,418 Patented. Nov. 16, 1965 ice operated in unison for manual operation of the multipole breaker.

For a better understanding of the nature and objects of the invention, reference may be had to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a View, in side elevation, of a single pole circuit breaker embodying the principal features of the invention;

FIG. 2 is a top view of the circuit breaker shown in FIG. 1;

FIG. 3 is an enlarged elevational view, with one of the insulating side plates removed, of the circuit-breaker mechanism;

FIG. 4 is a top view of the mechanism shown in FIG. 3; both of the side plates being shown, but the operating handle and associated parts being removed for the purpose of clarity;

FIG. 5 is an elevational View of one of the insulating side plates shown in FIGS. 3 and 4;

FIGS. 6, 7 and S are elevational, end and top views, respectively, of one of the supporting clips shown in FIG. 4;

FIGS. 9 and l0 are elevational, and end views, respectively, of the main latch member shown in FIG. 3;

FIGS. l1 and 12 are elevational and end views, respectively, of the trip member shown in FIG. 3;

FIGS. 13 and 14 are elevational and end views, respectively, of the larmature member shown in FIG. 3;

FIG. 15 is a top view of one of the plates of the arcextinguishing structure shown in FIGS. 3 and 4;

FIG. 16 is a top view of a three-pole circuit breaker illustrating features of the invention;

FIG. 17 is a top view of a two-pole circuit breaker illustrating features of the invention;

FIG. 18 is an elevational View of one of the handle ties shown in FIGS. 16 and 17; and

FIGS. 19 and 20 are elevational and end views, respectively, of one of the trip pin connecting members shown in FIGS. 16 and 17.

Certain features of the circuit breaker of this invention are described and claimed in the patent to Russell C. Strother et al., Patent No. 3,174,024, issued March 16, 1965, and assigned to the assignee of the instant application.

Referring to the drawings, a circuit breaker 3 is shown in FIGS. 1 and 2 comprising a housing 5 of molded insulating material, and a unitary circuit-breaker mechanism 7 supported within the housing. As seen in FIG. 2, the housing 5 comprises two halves 9 and 11 that are secured together by means of four tubular rivets 12 (FIGS. 1 and 2).

The unitary circuit-breaker mechanism 7, FIGS. 3 and 4, comprises a contact structure 13, an arc-extinguishing structure 15, an operating mechanism 17 and a tripping mechanism 19. The circuit-breaker mechanism is sup,- ported between two insulating side plates 21, one of which side plates 21 is shown in detail in FIG. 5.

The contact structure 13 comprises a stationary contact 23 and two movable contacts 25, only one of the movable contacts 25 being shown in FIG. 3. Each of the movable contacts 25 is supported on one end of a movable contact arm 2'7 (FIGS. 3 and 4). One end of a tension spring 29 is supported at the other ends of the two movable contact arms 27 on a pin 31 that connects the two movable contact arms. The other end of the spring 29 is attached to a pin 3.3 that is supported in openings 3S (FIG. 5) in the two insulating side plates 21. The pin 33 is positioned in suitable slots in the movable contact arms 27 so that the movable contact arms 27 can move relative to the pin 33 when the contact arms are in the closed position. The spring 29 biases the contact .3 arms 27 about a pivot pin 3'7 to provide contact pressure when the contacts 23, 25 are in the closed position. The contact structure is described and claimed in the hereinbefore mentioned copending application of Russell C. Strother et al.

The operating mechanism 17 includes a toggle, comprising a lower toggle link 38 that is pivotally connected to the movable contact arms 27 intermediate the ends of the Contact arms 27 by means of the pivot pin 37. An upper toggle link 39 is connected at one end to the upper end of the lower toggle link 38 by means of a knee pivot pin 41. The upper end of the upper toggle link 39 is pivotally connected to a releasable latch member 43 by means of a pivot pin 45. The releasable member 43 is pivotaly supported between the insulating side plates 21 by means of a pivot pin 47 that is supported in openings 49 (FIG. 5) in the side plates 21.

An operating member 51, having an inverted U-shaped construction is pivotally supported on the insulating side plates 21 in grooves 53 (FIG. 5). The legs of the U- shaped member 51 are prevented from moving olf of the top surface of the insulating side plates 21 by means of clips 55 (FIGS. 6 8) each of which clips is held in place by the pin 33 (FIGS. 3 and 4). The pin 33 extends through an opening 59 (FIG. 6) in each of the clips 55 and is riveted over at its ends as seen in FIG. 4. Each of the clips 55 has an opening 61 (FIG. 8) therein for receiving one of the legs of the U-shaped member 51.

An operating handle 63, of molded insulating material, is supported at the outer end of the U-shaped member 51. An arcuate portion 65 of the operating handle 63 substantially closes an opening in the molded housing (FIGS. l and 2) through which the operating handle 63 extends. Four springs 67 (only two of which are shown in FIG. 3) are connected at one end to two plates 68 (only one being shown in FIG. 3) that are connected to the knee pivot 41 of the toggle link 38, 39. The springs 67 are connected at their other ends to an inverted U- shaped plate 69 that is supported at the outer end of the U-shaped member 51.

The contacts 23, are manually opened by movement of the operating handle 63 in a counterclockwise (FIG. 3) direction to the off position. This movement carries the line of the action of the over-center springs 67 to the left of the pivot 41 causing collapse of the toggle 38, 39. As the toggle 38, 39 collapsesthe switch arms 27 first move to engage the pin 33 and thereafter the switch arms 27 rotate counterclockwise about the pin 33 to open the contacts 23, 25 with a snap action. Opening movement of the contact arms 27 is limited by er1- gagement of the contact arms with a pin 70 (FIGS. 3 and 4) which pin 70 is supported in openings 71 (FIG. 5) in the side plates 21. Reverse or clockwise movement of the operating handle 63 to the on position moves the knee pivot 41 of the toggle 3S, 39 to the right (FIG. 3) resetting the toggle 38, 39 and moving the Contact arms 27 back to the closed position, shown in FIG. 3, with a snap action.

The trip structure 19 comprises a trip member 73 that is seen in detail in FIGS. 11 and 12. The trip member 73 comprises a generally cylindrical trip bar 75 having a notch 77 therein, and a trip arm 79 having a flag portion 81 at the top thereof. The trip bar 75 is rotatably supported in openings 33 (FIG. 5 in the side plates 21. The ends of the trip bar 85 are cut away at 86 for a purpose to be hereinafter specifically described.

A main latch 87, which is seen in detail in FIGS. 9 and 10, comprises a pin SS that is rotatably supported in openings 89 (FIG. 5) in the side plates 21. The main latch 87 has a latch portion 91 that engages a latch portion 93 (FIG. 3) on the releasable member 43 to hold the releasable member in the latched position. The main latch 87 has a portion 95 that engages the periphery of the trip bar 75 just opposite the notch 77 (FIG. 12) when the parts are in the latched position (FIG. 3). The

trip member 73 is biased in a counterclockwise direction (FIG. 3) by means of a torsion spring 97. The main latch 87 is biased in a counterclockwise direction by means of a torsion spring 99.

An armature member 101 (seen in detail in FIGS. 13 and 14) comprises a pin 103 Iand a member 105 that has an armature 107 disposed at one end thereof and a projection 109 at the other end. The pin 103 of the armature member 101 is rotatably supported in openings 111 (FIG. 5) in the insulating side plates 21. The armature member 101 is biased in a counterclockwise direction (FIG. 3) by means of a torsion spring 112.

A bimetallic member 115 is attached at one end to a conductor 117. The free end of the bimetal 115 has a projection 119 thereon having a tapped opening through which an adjusting or Calibrating screw 121 extends. A U-shaped magnetic yoke 123 is attached to the conductor 117 opposite the armature 107.

The circuit through the circuit breaker mechanism (FIG. 3) extends from a conductor 127 that is attached at one end to the upper end of the conductor 117, through the conductor 117, exible conductors 129 that are attached at one end to the conductor 117 and at the other end to the contact arms 27, the contact arms 27, the contacts 23, 25 and a conductor 131.

Solderless terminal connectors 132 (FIG. 1), of a type well known in the art, are attached to the outer ends of the conductors 127 and 131 and are provided to enable connection of the circuit breaker 3 in an electrical circuit in `a manner well known in the art.

The conductor 117 has three projections 133 (FIG. 3) at each side thereof which projections fit in openings 134 (FIG. 5) in the side plates 21 to support the conductor 117, and the parts that are connected thereto, on the side plates 21. The conductor 131 has two projections 135 and 136 (FIG. 3) at each side thereof which projections fit in openings 137 `and 138 (FIG. 5), respectively, in the side plates 21 to support the conductor 131 and the parts that are connected to the conductor 131, on the side plates 21.

Two openings 139 (FIG. S) are provided in each of the side plates 21. When the circuit-breaker mechanism 7 (FIGS. 3 and 4) is mounted in the insulating housing 5 (FIGS. 1 and 2), two projections (not shown) that are molded integral with each of the halves 9 and 11 of the insulating housing 5, lit within the openings 139 in the side plates 21 to position and support the circuitbreaker mechanism 7 within the housing.

When an overload current below a predetermined value passes through the circuit breaker, the bimetallic member 115 is heated and it bends to the right (FIG. 3) whereupon the Calibrating screw 121 engages the flag portion 81 of the trip member 73 rotating the trip member 73 in a clockwise direction about the pivot 75. Dur ing this movement, the portion 95 of the main latch 87 rides off of the periphery of the trip bar 75 and snaps clockwise into the notch 77 (FIG. 112) of the trip bar 75. During this clockwise movement of the main latch 87, the latch portion 91 thereon rotates free of the latch portion 93 of the releasable member 43 to release the member 43. When released, the member 43 rotates clockwise about its pivot 47 under the bias of the springs 67, causing collapse of the toggle 38, 39 and opening of the switch arms 27 about the pivot 33. During this movement, the handle 63 is moved, in a manner well known in the art, to a tripped position intermediate the on and olf positions, thereby giving a visual indication that a tripping operation has occured.

Before the contacts can be closed following an automatic opening operation. it is necessary to reset and relatch the mechanism. This is accomplished by moving the handle 63 in a counterclockwise direction from the intermediate or tripped position to the extreme oli position. During this movement, a projection 140 on the U-shaped member 51 engages a shoulder 141 on the releasable member 43 moving the releasable member 43 counterclockwise about its pivot 47. Near the end of this movement, the lower rounded part of the latch portion 93 of the releasable member 43 engages an outwardly extending arm 142 on the main latch 87 and moves the main latch to the latching position. As soon as the portion 95 of the main latch 87 clears the edge adjacent the notch 77 (FIG. 12) of the trip bar 75, the torsion spring 97 (FIG. 3) rotates the trip member 73 clockwise to the latched position. The latch portion 91 of the main latch 87 is then in position engaging the latch portion 93 of the releasable member 43 so that upon release of the handle 63, the mechanism is latched and the contacts can be closed in the previously described manner by movement of the handle 63 to the on position.

Upon the occurrence of an overload current above the predetermined value, the magnetic yoke 123 is energized sufficiently to attract the armature 107 to rotate the armature 101 clockwise about its pivot 103, whereupon the upper projection 109 on the armature member 101 engages the ag portion 81 of the trip member 73 rotating the trip member 73 clockwise to effect release of the main latch 87 and release of the releasable member 43 to thereby effect a tripping operation in the same manner hereinbefore described.

When the contacts 23, 25 open, an arc is established between each of the movable contacts 25 and the stationary contact 23. These arcs are extinguished by means of the arc-extinguishing structure 15. The arc-extinguishing structure comprises the two insulating side plates 21, a plurality of arc-extinguishing members or plates 151 (oneA of which is shown in detail in FIG. 15), an arcrunner plate 152 that is connected to the stationary contact 23, a plate 153 backing up the are runner plate 152, two insulating plates 154 and an insulating plate 155. Each of the arc-extinguishing plates 151 has two notches 159 (FIG. 15 therein. Each of the arc-extinguishing plates 151 is supported between the insulating side plates 21 by means of elongated projections 161 (FIG. 15) that t in the openings 163 (FIG. 5) in the side plates 21. Projections 162 on each side of the arc-runner plate 152 and on each side of the arc-runner supporting plate 153 it in the openings 138 (FIG. 5) in the insulating side plates 21 to support the plates 152 and 153 on the side plates 21.

The arc-extinguishing plates 151 of the arc-extinguishing structure 15 can ibe of insulating material to elongate the arcs for extinction. Preferably, however, the plates are of a magnetic and conducting material such as steel to draw the arcs into the plates where they are broken up into a plurality of short serially related arcs that are extinguished in a manner well known in the art. A detailed description of the theory of arc-interruption is set forth in the patent to I. A. Kalaway, Patent No. 2,590,543, issued March 25, 1952, and assigned to the assignee of the instant application.

During the opening operation, when the contact arms 27 move away from the contact 23, the two arcs established between the two contacts 25 and the contact 23, are magnetically attracted along the arc-runner plate 152 and into the slots 159 (FIG. 15 of the magnetic plates 151 to be broken up into a plurality of serially related arc portions, which arc portions are rapidly extinguished in a manner well known in the art.

The insulating plates 154 and 155 have projections 171 thereon that engage in openings 137 and 173 (FIG. 5) in the insulating side plates 21 to support the plates 154 and 155 on the side plates 21. These insulating members 154, 155 are provided to block the gases, that are generated upon extinguishment of the arc, from moving back into the operating portion of the circuit breaker.

Advantages of making the circuit-breaker mechanism as a unitary operating structure are as follows: The mechanism can be tested and calibrated prior to its being mounted within the insulating housing. Assembly is easier since there is convenient 'access to the parts. The calibration is automatically sealed when the mechanism is mounted in the housing. If the molded housing is broken during or after assembly, the mechanism can be salvaged as a unit that is calibrated and ready to be mounted in another housing. Since the mechanism functions as a unitary operating structure, shrinkage or Warpage of the molded insulating housing will have little effect on the calibration of the circuit breaker.

In FIG. 17 there is illustrated a two-pole circuit breaker or circuit interrupter 170 comprising two identical circuit breakers 3 that are secured together in an abutting side-by-side relationship by means of rivets 171 that pass through the tubular rivets 12 of the individual breakers. A handle tie 173 having ends 175 that engage in openings 177 (FIG. 3) in the handles 63 is provided to tie the handles 63 of the circuit breakers 3 together to move as a unitary structure. Thus, both poles of the multipole circuit breaker can be simultaneously manually moved to open and close the breaker. Referring to FIG. 4, it will be seen that the ends of the trip member 73 extend out a shortdistance from the side plates 21. The tripping mechanisms 19 of both pole units (FIG. 17) of the two pole circuit breaker are tied together by means of a trip bar connecting member 179. The trip bar connecting member 179 has openings 181 (FIGS. 19 and 20) therein which openings are shaped to key with the ends 85 (FIG. 12) of the trip members 73.

Each half 9 and 11 (FIG. 2) of the molded housing 5 of each of the circuit breakers 3 (FIG. 17 is provided with a knockout 180 (FIG. l) that is removable to provide access to an end 85 (FIG. l2) of the trip bar 75. As seen in FIG. 17, when the breakers 3 are connected together the adjacent knockouts 180 (FIG. 1) are removed and the trip bar connecting member 179 is placed in position with the openings 181 therein receiving the adjacent ends 85 of the trip bars 75. With the connecting member 179 in place (FIG. 17) the two trip members 73 (FIGS. 11 and l2) of the two pole units 3 will move as a common unitary trip structure, so that upon the occurrence of a tripping overcurrent in either of the pole units 3, both pole units will be automatically opened.

A three-pole circuit breaker or circuit interrupter 185 is shown in FIG. 16 and comprises three identical circuit breakers 3 fastened together by means of elongated rivets 187 that pass through the tubular rivets 12 of the individual circuit breakers. Thesel three circuit breakers or pole units are tied together by means of two handle ties 173 and two trip-bar connecting members 179 in the same manner as the two pole units of the two-pole circuit breaker (FIG. 17) are connected.

With the provision of a knockout (FIG. l) in each.

side of each circuit breaker 3, and with the trip bar 75 having its ends 85 (FIG. 4) extending out through both of the side plates 21, each of the circuit breakers 3 (FIGS. l, 16 and 17) is adapted to be connected at either side thereof to another circuit breaker. It is to be noted also that each pole unit 3 of the multi-pole circuit breakers 170 and 185, is a unit that is manufactured as a separate single pole circuit breaker and can be utilized as a separate single pole breaker.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details and arrangement of parts thereof may lhe made without departing from some of the essential features of the invention.

We claim as our invention:

1. A circuit breaker comprising an insulating housing; a unitary circuit breaker mechanism supported within said housing; said unitary circuit breaker mechanism comprising insulating side plates and circuit interrupting means supported by said insulating side plates; said circuit interrupting means comprising a pair of contacts openable to establish an arc therebetween, an overcenter spring operating mechanism, manually operable means for operating said spring operating mechanism between overcenter positions to open and close said contacts, trip means operable automatically upon the occurrence of certain abnormal conditions to effect a tripping operation of said spring operating mechanism to open said contacts, said insulating side plates having a plurality of openings therein, arc-extinguishing means comprising a plurality of fiat arc-extinguishing plates each of which has a projection at each of two opposite sides thereof, each of said arc-extinguishing plates having a slot therein, said arc-extinguishing plates being supported on and between said insulating side plates in a spaced stacked condition with said slots being in general alignment, during separation of said contacts one of said contacts moving generally within said aligned slots to establish an arc which arc is extinguished by means of said stacked arc-extinguishing plates, and said projections tting in said openings to thereby support said arc-extinguishing plates on and between said insulating side plates.

2. A circuit breaker comprising an insulating housing; a unitary circuit -breaker mechanism supported within said housing; said unitary circuit breaker mechanism comprising a pair of spaced insulating side plates and circuit interrupting means supported on said insulating side plates; said circuit interrupting means comprising at least two contacts openable to interrupt the circuit, an overcenter spring operating mechanism, manually operable means for operating said spring operating mechanism between overcenter positions to open and close said contacts, trip means operable automatically upon the occurrence of certain abnormal conditions to effect a tripping operation of said spring operating mechanism to open said contacts, arc-extinguishing means comprising a plurality of flat arc-extinguishing plates of magnetic material each of which has a projection at each of two opposite sides thereof, each of said arc-extinguishing plates having a slot therein, said arc-extinguishing plates being supported between said insulating side plates in a spaced stacked condition with said slots being in general alignment, during circuit interruption one of said contacts moving generally within said aligned slots to establish an arc between said contacts which arc is magnetically drawn into said arc-extinguishing plates to be extinguished, each of said insulating side plates having opening means therein, said projections being disposed within said opening means to thereby support said plu- -rality of arc-extinguishing plates between said insulating side plates.

References Cited by the Examiner UNITED STATES PATENTS 2,065,357 12/1936 Von Hoorn 200-116 2,174,232 9/1939 Baker 200-116 X 2,371,738 3/1945 Christoierson 200-116 2,494,315 1/1950 Rowe 200-144 X 2,590,543 3/1952 Kalaway 200-144 2,707,218 4/1955 Cellerini 200--144 2,769,066 10/1956 Cellerini 200--147 2,824,191 2/1958 Christensen 200-116 i 2,889,428 6/1959 Kingdom et al. 200-116 3,031,552 4/1962 Stewart 200-144 3,174,024 3/1965 Strothers et al 200-116 X KATHLEEN H. CLAFFY, Primary Examiner.

BERNARD A. GILHEANY, ROBERT K. SCHAEFER,

Exmniizers. 

1. A CIRCUIT BREAKER COMPRISING AN INSULATING HOUSING; A UNITARY CIRCUIT BREAKER MECHANISM SUPPORTED WITHIN SAID HOUSING; SAID UNITARY CIRCUIT BREAKER MECHANISM COMPRISING INSULATING SIDE PLATES AND CIRCUIT INTERRUPTING MEANS SUPPORTED BY SAID INSULATING SIDE PLATES; SAID CIRCUIT INTERRUPTING MEANS COMPRISING A PAIR OF CONTACTS OPENABLE TO ESTABLISH AN ARC THEREBETWEEN, AN OVERCENTER SPRING OPERATING MECHANISM, MANUALLY OPERABLE MEANS FOR OPERATING SAID SPRING OPERATING MECHANISM BETWEEN OVERCENTER POSITIONS TO OPEN AND CLOSE SAID CONTACTS, TRIP MEANS OPERABLE AUTOMATICALLY UPON THE OCCURRENCE OF CERTAIN ABNORMAL CONDITIONS TO EFFECT A TRIPPING OPERATION OF SAID SPRING OPERATING MECHANISM TO OPEN SAID CONTACTS, SAID INSULATING SIDE PLATES HAVING A PLURALITY OF OPENINGS THEREIN, ARC-EXTINGUISHING MEANS COMPRISING A PLURALITY OF FLAT ARC-EXTINGUISHING PLATES EACH OF WHICH HAS A PROJECTION AT EACH OF TWO OPPOSITE SIDES THEREOF, EACH OF SAID ARC-EXTINGUISING PLATES HAVING A SLOT THEREIN, SAID ARD-EXTINGUISHING PLATES BEING SUPPORTED ON AND BETWEEN SAID INSULATING SIDE PLATES IN A SPACED STACKED CONDITION WITH SAID SLOTS BEING IN GENERAL ALIGNMENT, DURING SEPARATION OF SAID CONTACTS ONE OF SAID CONTACTS MOVING GENERALLY WITHIN SAID ALIGNED SLOTS TO ESTABLISH AN ARC WHICH ARC IS EXTINGUISHED BY MEANS OF SAID STACKED ARC-EXTINGUISHING PLATES, AND SAID PROJECTIONS FITTING IN SAID OPENINGS TO THEREBY SUPPORT SAID ARC-EXTINGUISHING PLATES ON AND BETWEEN SAID INSULATING SIDE PLATES. 